In conventional jaw crushers, a moving jaw is supported at its lower end by a plate type structure which is commonly known as a toggle plate. The upper end of the moving jaw is controlled by an elliptical drive, causing the jaw to move back and forth, relative to a fixed jaw. The jaw crusher can be a single toggle design or a double toggle design.
Our U.S. Pat. No. 4,927,089, which is incorporated herein by reference, discloses a hydraulic control system which replaces the rigid toggle plate of the prior art. This hydraulic control arrangement allows adjustment of the bite between the moving jaw and the fixed jaw. With the hydraulic control arrangement adjustment of the bite can be carried out during operation of the rock crusher. Such adjustment is desirable to maintain a desired throughput through the rock crusher, and this throughput varies as a function of the amount of material received and the type and size of the material. The adjustable bite provides the operator with an on the fly adjustment that directly affects the throughput of the rock crusher and also simplifies clearing of the rock crusher in the event of a non-crushable material becoming lodged in the bite.
The hydraulic ram disclosed in our patent is a double acting arrangement and includes a safety relief arrangement in the event of a non-crushable material being encountered.
Adjustment of the hydraulic control arrangement to vary the bite also varies a tensioning arrangement of the jaw crusher. The tensioning arrangement includes two coil springs used to apply a force on tension rods of the rock crusher attached near the base of the movable jaw. Although it would be desirable to have a constant tensioning force, adjustment of the hydraulic cylinders causes a change in the tensioning force. This can be corrected by manually adjusting adjustment nuts at the end of the tension rods, however, this is typically not practical with the rock crusher in operation. There have been proposals to use hydraulic cylinders for maintaining a constant tensioning force, however, these systems often have not proven entirely satisfactory, and appreciably add to the cost of the system.